No wonder Darcy looks gloomy at her outburst. After all, she never exposed Wickham's character out of respect for Georgiana's reputation and his request for discretion. Part of him must wonder if she blames him, and part of him must be taking some of the blame on himself. Not that he deserves any blame, but the sight of Elizabeth in tears, feeling guilty for honouring his privacy, hits him where it hurts.